I think that all of the Star Wars movies have been intended to appeal to the broadest audience as possible, but that the increased disposable income of the younger section of that audience probably did lead to the prequels catering to it more specifically. I think the OT would best be described as a "family adventure", and perhaps the prequels failed to remember the rest of the family, to an extent. It is probably the better quality of the OT that, overall, leads to it possessing an enduring cross-generational appeal.

In thirty years time, I can't honestly envision the prequels being remembered or watched as anything other than a bittersweet footnote to the OT.